1. Field of the Invention
The present invention relates to a measurement apparatus that measures the position or attitude of a measurement target.
2. Description of the Related Art
In recent years, a complex task such as the assembly process of an industrial product, which is traditionally performed by a human, is done by a robot instead. The robot performs assembly by gripping a part by an end effector such as a hand. To implement such assembly, the position or attitude of an article (work) to be gripped needs to be measured.
For example, Japanese Patent No. 5393318 proposes a technique of measuring the position or attitude of a work by model fitting using measurement information (edge data) obtained from a grayscale image and measurement information (distance point group data) obtained from a range image. In this technique, the position or attitude of a work is estimated using maximum likelihood estimation, assuming that an error in the grayscale image and an error in the range image comply with different probability distributions. Hence, even if the initial condition is poor, the position or attitude of the work can stably be estimated.
Consider a case in which the position or attitude of a work is measured while moving a robot to speed up the assembly process. In this case, to guarantee the field shift between a grayscale image and a range image, it is necessary to simultaneously obtain the grayscale image and the range image. Japanese Patent No. 5122729 proposes a technique of simultaneously illuminating a work with light beams of different wavelengths using a grayscale image illumination unit and a range image illumination unit, separating the light beams of the wavelengths by a wavelength separation prism, and simultaneously capturing both images using a grayscale image sensor and a range image sensor.
However, the technique disclosed in Japanese Patent No. 5122729 needs a sensor for each of the grayscale image and the range image. Hence, problems (1), (2) and (3) arise.
(1) Since a plurality of sensors are necessary, the apparatus cost rises.
(2) Since a plurality of sensors need to be arranged, the apparatus size becomes large.
(3) Since a grayscale image and a range image are obtained by separate sensors, stability to a temperature variation such as heat generation of the illumination units or sensors poses a problem.